The present invention relates to a control apparatus for synchronous motors and more particularly to a synchronous motor control apparatus which is low in cost and simple in construction and is capable of easily effecting the required speed control.
It has been difficult in the past to start synchronous motors and the synchronous motors have required special starting devices thus making them complicated in construction and high in cost.
Also, it has been difficult to control the speed of the synchronous motor over a wide range of high to low speeds since the load current increases with a decrease in the motor speed.
In addition, the synchronous motor has heretofore used permanent magnets for its rotor and the use of powerfull magnets has been required for reducing the size of the motor and increasing the efficiency of the motor, thus increasing the cost extremely due to the use of rare earth magnets for the purpose.